There is a plethora of references (both patents and literature articles) dealing with the formation of acids, one of the most important being adipic acid, by oxidation of hydrocarbons. Adipic acid is used to produce Nylon 66 fibers and resins, polyesters, polyurethanes, and miscellaneous other compounds.
There are different processes of manufacturing adipic acid. The conventional process involves a first step of oxidizing cyclohexane with oxygen to a mixture of cyclohexanone and cyclohexanol (KA mixture), and then oxidation of the KA mixture with nitric acid to adipic acid. Other processes include, among others, the "Hydroperoxide Process", the "Boric Acid Process", and the "Direct Synthesis Process", which involves direct oxidation of cyclohexane to adipic acid with oxygen in the presence of solvents, catalysts, and promoters.
The Direct Synthesis Process has been given attention for a long time. However, to this date it has found little commercial success. One of the reasons is that although it looks very simple at first glance, it is extremely complex in reality. Due to this complexity, one can find strikingly conflicting results, comments, and views in different references.
It is well known that after a reaction has taken place according to the Direct Synthesis, a mixture of two liquid phases is present at ambient temperature, along with a solid phase mainly consisting of adipic acid. The two liquid phases have been called the "Polar Phase" and the "Non-Polar Phase". However, no attention has been paid so far to the importance of the two phases, except for separating the adipic acid from the "Polar Phase" and recycling these phases to the reactor partially or totally with or without further treatment.
It is also important to note that most studies on the Direct Oxidation have been conducted in a batch mode, literally or for all practical purposes.
There is a plethora of references dealing with oxidation of organic compounds to produce acids, such as, for example, adipic acid and/or intermediate products, such as for example cyclohexanone, cyclohexanol, cyclohexylhydroperoxide, etc.
The following references, among the plethora of others, may be considered as representative of oxidation processes relative to the preparation of diacids and intermediate products.
U.S. Pat. No. 5,463,119 (Kollar) discloses a process for the oxidative preparation of C.sub.5 -C.sub.8 aliphatic dibasic acids by
(1) reacting, PA1 (2) removing the aliphatic dibasic acid; and PA1 (3) recycling intermediates, post oxidation components, and derivatives thereof remaining after removal of the aliphatic dibasic acid into the oxidation reaction. PA1 (1) reacting, at a cycloaliphatic hydrocarbon conversion level of between about 7% and about 30%, PA1 (2) isolating the C5-C8 aliphatic dibasic acid. PA1 (a) contacting the liquid mixture with a gaseous oxidant in the reaction zone at a first temperature, the first temperature being adequately high for the oxidation to proceed; PA1 (b) controlling the solvent to hydrocarbon ratio within a range at which reaction rate and/or reactivity is substantially maximized at the desired levels of catalyst, water, and initiator. PA1 (a) if the reaction rate and/or reactivity increases, continuing to increase the solvent to hydrocarbon ratio to a point that no further increase in reaction rate and/or reactivity is realized; and PA1 (b) if the reaction rate and/or reactivity decreases, lowering the solvent to hydrocarbon ratio, and if the reaction rate and/or reactivity increases, continuing to decrease the solvent to hydrocarbon ratio to a point that no further increase in reaction rate and/or reactivity is realized. PA1 (a) if the reaction rate and/or reactivity increases, continuing to decrease the solvent to hydrocarbon ratio to a point that no further increase in reaction rate and/or reactivity is realized; PA1 (b) if the reaction rate and/or reactivity decreases, increase the solvent to hydrocarbon ratio, and if the reaction rate and/or reactivity increases, continuing to increase the solvent to hydrocarbon ratio to a point that no further increase in reaction rate and/or reactivity is realized. PA1 (a) contacting the liquid mixture with a gaseous oxidant in the reaction zone at a first temperature, the first temperature being adequately high for the oxidation to proceed; and PA1 (b) controlling the solvent to hydrocarbon ratio in a manner that reaction rate and/or reactivity is substantially maintained within a desired reaction rate and/or reactivity range, or in a manner that the reaction rate and/or reactivity is directed toward said reaction rate and/or reactivity range if the reaction rate and/or reactivity is outside the desired reaction rate and/or reactivity range at the initial solvent to hydrocarbon ratio, at the desired levels of catalyst, water, and initiator. PA1 (a) if the reaction rate and/or reactivity moves toward the desired reaction rate and/or reactivity range, continuing to increase the solvent to hydrocarbon ratio to a point that the reaction rate and/or reactivity falls within said desired reaction rate and/or reactivity range or to a point that the reaction rate and/or reactivity does not move further toward the desired reaction rate and/or reactivity range; and PA1 (b) if the reaction rate and/or reactivity moves away from the desired reaction rate and/or reactivity range, lowering the solvent to hydrocarbon ratio, and if the reaction rate and/or reactivity moves toward the desired reaction rate and/or reactivity range, continuing to decrease the solvent to hydrocarbon ratio to a point that the reaction rate and/or reactivity falls within said desired reaction rate and/or reactivity range or to a point that the reaction rate and/or reactivity does not move further toward the desired reaction rate and/or reactivity range. PA1 (a) if the reaction rate and/or reactivity moves toward the desired reaction rate and/or reactivity range, continuing to decrease the solvent to hydrocarbon ratio to a point that the reaction rate and/or reactivity falls within said desired reaction rate and/or reactivity range or to a point that the reaction rate and/or reactivity does not move further toward the desired reaction rate and/or reactivity range; and PA1 (b) if the reaction rate and/or reactivity moves away from the desired reaction rate and/or reactivity range, increasing the solvent to hydrocarbon ratio, and if the reaction rate and/or reactivity moves toward the desired reaction rate and/or reactivity range, continuing to increase the solvent to hydrocarbon ratio to a point that the reaction rate and/or reactivity falls within said desired reaction rate and/or reactivity range or to a point that the reaction rate and/or reactivity does not move further toward the desired reaction rate and/or reactivity range.
(a) at least one saturated cycloaliphatic hydrocarbon having from 5 to 8 ring carbon atoms in the liquid phase and PA2 (b) an excess of oxygen gas or an oxygen-containing gas in the presence of PA2 (c) a solvent comprising an organic acid containing only primary and/or secondary hydrogen atoms and PA2 (d) at least about 0.002 mole per 1000 grams of reaction mixture of a polyvalent heavy metal catalyst; PA2 (a) at least one saturated cycloaliphatic hydrocarbon having from 5 to 8 ring carbon atoms in the liquid phase and PA2 (b) an excess of oxygen gas or an oxygen containing gas mixture in the presence of PA2 (c) less than 1.5 moles of a solvent per mole of cycloaliphatic hydrocarbon (a), wherein said solvent comprises an organic acid containing only primary and/or secondary hydrogen atoms and PA2 (d) at least about 0.002 mole per 1000 grams of reaction mixture of a polyvalent heavy metal catalyst; and
U.S. Pat. No. 5,374,767 (Drinkard et al) discloses formation of cyclohexyladipates in a staged reactor, e.g., a reactive distillation column. A mixture containing a major amount of benzene and a minor amount of cyclohexane is fed to the lower portion of the reaction zone and adipic acid is fed to the upper portion of the reaction zone, cyclohexyladipates are formed and removed from the lower portion of the reaction zone and benzene is removed from the upper portion of the reaction zone. The reaction zone also contains an acid catalyst.
U.S. Pat. No. 5,321,157 (Kollar) discloses a process for the preparation of C.sub.5 -C.sub.8 aliphatic dibasic acids through oxidation of corresponding saturated cycloaliphatic hydrocarbons by
U.S. Pat. No. 5,221,800 (Park et al) discloses a process for the manufacture of adipic acid. In this process, cyclohexane is oxidized in an aliphatic monobasic acid solvent in the presence of a soluble cobalt salt wherein water is continuously or intermittently added to the reaction system after the initiation of oxidation of eyelohexane as indicated by a suitable means of detection, and wherein the reaction is conducted at a temperature of about 50.degree. C. to about 150.degree. C. at an oxygen partial pressure of about 50 to 420 pounds per square inch absolute.
U.S. Pat. No. 4,263,453 (Schultz et al) discloses a process claiming improved yields by the addition of water at the beginning of the reaction, generally of the order of 0.5 to 15% relative to monobasic aliphatic acid solvent, and preferably 1 to 10% relative to the solvent.
U.S. Pat. No. 3,987,100 (Barnette et al.) describes a process of oxidizing cyclohexane to produce cyclohexanone and cyclohexanol, said process comprising contacting a stream of liquid cyclohexane with oxygen in each of at least three successive oxidation stages by introducing into each stage a mixture of gases comprising molecular oxygen and an inert gas.
U.S. Pat. No. 3,957,876 (Rapoport et al.) describes a process for the preparation of cyclohexyl hydroperoxide substantially free of other peroxides by oxidation of cyclohexane containing a cyclohexane soluble cobalt salt in a zoned oxidation process in which an oxygen containing gas is fed to each zone in the oxidation section in an amount in excess of that which will react under the conditions of that zone.
U.S. Pat. No. 3,932,513 (Russell) discloses the oxidation of cyclohexane with molecular oxygen in a series of reaction zones, with vaporization of cyclohexane from the last reactor effluent and parallel distribution of this cyclohexane vapor among the series of reaction zones.
U.S. Pat. No. 3,530,185 (Pugi) discloses a process for manufacturing precursors of adipic acid by oxidation with an oxygen-containing inert gas which process is conducted in at least three successive oxidation stages by passing a stream of liquid cyclohexane maintained at a temperature in the range of 140.degree. to 200.degree. C. and a pressure in the range of 50 to 350 p.s.i.g. through each successive oxidation stage and by introducing a mixture of gases containing oxygen in each oxidation stage in an amount such that substantially all of the oxygen introduced into each stage is consumed in that stage thereafter causing the residual inert gases to pass countercurrent into the stream of liquid during the passage of the stream through said stages.
U.S. Pat. No. 3,515,751 (Oberster et al) discloses a process for the production of epsilon-hydroxycaproic acid in which cyclohexane is oxidized by liquid phase air oxidation in the presence of a catalytic amount of a lower aliphatic carboxylic acid and a catalytic amount of a peroxide under certain reaction conditions so that most of the oxidation products are found in a second, heavy liquid layer, and are directed to the production of epsilon-hydroxycaproic acid.
U.S. Pat. No. 3,390,174 (Schultz et al) discloses a process claiming improved yields of aliphatic dibasic acids when oxidizing the respective cyclic hydrocarbons at temperatures between 130.degree. and 160.degree. C., while removing the water of reaction substantially as quickly as it is formed.
U.S. Pat. No. 3,361,806 (Lidov et al) discloses a process for the production of adipic acid by the further oxidation of the products of oxidation of cyclohexane after separation of cyclohexane from the oxidation mixture, and more particularly to stage wise oxidation of the cyclohexane to give high yields of adipic acid precursors and also to provide a low enough concentration of oxygen in the vent gas so that the latter is not a combustible mixture.
U.S. Pat. No. 3,234,271 (Barker et al) discloses a process for the production of adipic acid by the two-step oxidation of cyclohexane with oxygen. In a preferred embodiment, mixtures comprising cyclohexanone and cyclohexanol are oxidized. In another embodiment, the process involves the production of adipic acid from cyclohexane by oxidation thereof, separation of cyclohexane from the oxidation mixture and recycle thereof, and further oxidation of the other products of oxidation.
U.S. Pat. No. 3,231,608 (Kollar) discloses a process for the preparation of aliphatic dibasic acids from saturated cyclic hydrocarbons having from 4 to 8 cyclic carbon atoms per molecule in the presence of a solvent which comprises an aliphatic monobasic acid which contains only primary and secondary hydrogen atoms and a catalyst comprising a cobalt salt of an organic acid, and in which process the molar ratio of said solvent to said saturated cyclic hydrocarbon is between 1.5:1 and 7:1, and in which process the molar ratio of said catalyst to said saturated cyclic hydrocarbon is at least 5 millimoles per mole.
U.S. Pat. No. 3,161,603 (Leyshon et al) discloses a process for recovering the copper-vanadium catalyst from the waste liquors obtained in the manufacture of adipic acid by the nitric acid oxidation of cyclohexanol and/or cyclohexanone.
U.S. Pat. No. 2,565,087 (Porter et al) discloses the oxidation of cycloaliphatic hydrocarbons in the liquid phase with a gas containing molecular oxygen and in the presence of about 10% water to produce two phases and avoid formation of esters.
U.S. Pat. No. 2,557,282 (Ilamblet et al) discloses production of adipic acid and related aliphatic dibasic acids; more particularly to the production of adipic acid by the direct oxidation of cyclohexane.
U.S. Pat. No. 2,439,513 (Hamblet et al) discloses the production of adipic acid and related aliphatic dibasic acids and more particularly to the production of adipic acid by the oxidation of cyclohexane.
U.S. Pat. No. 2,223,494 (Loder et al) discloses the oxidation of cyclic saturated hydrocarbons and more particularly to the production of cyclic alcohols and cyclic ketones by oxidation of cyclic saturated hydrocarbons with an oxygen-containing gas.
U.S. Pat. No. 2,223,493 (Loder et al) discloses the production of aliphatic dibasic acids and more particularly to the production of aliphatic dibasic acids by oxidation of cyclic saturated hydrocarbons with an oxygen-containing gas.
German Patent DE 44 26 132 A1 (Kysela et al) discloses a method of dehydration of process acetic acid from liquid-phase oxidation of cyclohexane with air, in the presence of cobalt salts as a catalyst after separation of the adipic acid after filtration, while simultaneously avoiding cobalt salt precipitates in the dehydration column, characterized in that the acetic acid phase to be returned to the beginning of the process is subjected to azeotropic distillation by the use of added cyclohexane, under distillative removal of the water down to a residual content of less than [sic] 0.3-0.7%.
PCT International Publication WO 96/03365 (Constantini et al) discloses a process for recycling a cobalt-containing catalyst in a direct reaction of oxidation of cyclohexane into adipic acid, characterized by including a step in which the reaction mixture obtained by oxidation into adipic acid is treated by extraction of at least a portion of the glutaric acid and the succinic acid formed during the reaction.
None of the above references, or any other references known to the inventors disclose, suggest or imply, singly or in combination, control of oxidation reactions by adjusting the solvent to hydrocarbon ratio subject to the intricate and critical controls and requirements of the instant invention as described and claimed.
Our U.S. Pat. Nos. 5,580,531, 5,558,842, 5,502,245, and our co-pending applications Ser. No. 08/477,195 (filed Jun. 7, 1995), 08/587,967 (filed Jan. 17, 1996), and 08/620,974 (filed Mar. 25, 1996), all of which are incorporated herein by reference, describe methods and apparatuses relative to controlling reactions in atomized liquids. Our co-pending application, Docket No. T-603, Ser. No. 08/812847, filed on Mar. 6, 1997, and our co-pending application, Docket No. T-701, Ser. No. 08/824992, filed on Mar. 27, 1997 are both also incorporated herein by reference.
All of the following patent applications, which were filed simultaneously on May 21, 1997, are also incorporated herein by reference:
U.S. Pat. application Ser. No. 08/859,985 of Eustathios Vassiliou, Mark W. Dassel, David C. DeCoster, Ader M. Rostami, and Sharon M. Aldrich, titled "Methods and Devices for Controlling the Reaction Rate of a Hydrocarbon to an Intermediate Oxidation Product by Pressure Drop Adjustments";
U.S. Pat. application Ser. No. 08/861,281 of Mark W. Dassel, Eustathios Vassiliou, David C. DeCoster, Ader M. Rostami, and Sharon M. Aldrich, titled "Methods and Devices for Controlling the Reaction Rate of a Hydrocarbon to an Intermediate Oxidation Product by Monitoring Flow of Incoming and Outcoming Gases";
U.S. Pat. application Ser. No. 08/861,180 of David C. DeCoster, Ader M. Rostami, Mark W. Dassel, and Eustathios Vassiliou, titled "Methods and Devices for Controlling the Oxidation Rate of a Hydrocarbon by Adjusting the Ratio of the Hydrocarbon to a RateModulator";
U.S. Pat. application Ser. No. 08/861,176 of Mark W. Dassel, Eustathios Vassiliou, David C. DeCoster, and Ader M. Rostami, titled "Methods of Preparing an Intermediate Oxidation Product from a Hydrocarbon by Utilizing an Activated Initiator";
U.S. Pat. application Ser. No. 08/859,890 of Ader M. Rostami, Mark W. Dassel, Eustathios Vassiliou, David C. DeCoster, titled "Methods and Devices for Controlling the Oxidation of a Hydrocarbon to an Acid by Regulating Temperature/Conversion Relationship in Multi-Stage Arrangements"; and
U.S. Pat. application Ser. No. 08/861,210 of Eustathios Vassiliou, Ader M. Rostami, David C. DeCoster, and Mark W. Dassel, titled "Pseudo-Plug-Flow Reactor".
Further, our patent application having U.S. Pat. application Ser. No. 08/876,692, filed on Jun. 16, 1997, of Ader M. Rostami, David C. DeCoster, Eustathios Vassiliou, Mark W. Dassel, and Sharon M. Aldrich, titled "Methods and Devices for Controlling Hydrocarbon Oxidations to Respective Acids by Adjusting the Water Level during the Reaction" is also incorporated herein by reference.
In addition, our PCT patent application having International application No. PCT/US 97112944 filed on Jun. 23, 1996 of David C. DeCoster, Eustathios Vassiliou, Mark W. Dassel, Sharon M. Aldrich, and Ader M. Rostami, titled "Methods and Devices for Controlling the Reaction Rate and/or Reactivity of Hydrocarbon to an Intermediate Oxidation Product by Adjusting the Oxidant Consumption Rate" is also incorporated herein by reference.